The present invention relates to bicycle multi-gear cassettes, and more particularly, to a multi-gear cassette that includes a truncated conical shell, a plurality of toothed sprockets disposed thereon, a torque load transmitting profile, and a radial load transmitting profile wherein the shell, sprockets and load transmitting profiles embody a single piece.
In a conventional multi-gear bicycle cassette, a plurality of discrete sprockets of variable diameter are arranged radially about an axis of a wheel hub. Each sprocket has a plurality of teeth spaced around its periphery for engaging a bicycle chain. The sprockets are mountable to a hub driver mechanism of the wheel hub to transfer pedaling forces from the bicycle chain to the wheel hub. In conventional designs, each sprocket may include a torque and radial load transmitting profile that mates to a corresponding profile on the hub driver mechanism. One disadvantage of this design is that the sprockets are acting individually in transmitting pedaling load from the chain, at one end, to the hub driver mechanism, at the other end, making the sprockets vulnerable to buckling and thus requiring thicker and heavier sprockets than desired.
In other devices, the individual sprockets may be attached to a plurality of carrier arms of an intermediate carrier, the arms receiving loading from the sprockets and transmitting it to the hub driver mechanism. Although the carrier may provide some lateral support to the sprockets, the carrier arms may themselves twist and flex under loading, also leading to buckling. Carriers with more rigid arms provide additional buckling resistance but come with a weight penalty. Beyond being resistant to buckling, carrier and non carrier-based multi-gear cassettes must be sufficiently rigid to resist excessive twisting and flexing under high impact pedaling forces to provide positive and direct load transmission to the wheel hub.
In the carrier cassettes described above, the discrete sprockets are attached to the carrier arms using bolts, mating threads, coupling projections or the like. These mechanical connections not only require additional material on the mating pieces, making the sprocket assembly heavier, but also introduce hole and thread features that weaken the mating parts and provide possible fatigue and fracture failure points on both the sprockets and carrier. Finally, such mechanical connections also introduce additional unwanted flexibility as they twist and deform under loading, softening load transmission from the chain to the hub driver mechanism.
Accordingly, a single-piece cassette according to the present invention avoids these design limitations by providing a rigid, buckling-resistant and lightweight load transmission path from the chain to the hub driver mechanism. In the prior devices having discrete sprockets, with or without intermediate carriers, the user may selectively replace one or more of the individual sprockets to customize the gear ratios of the cassette. Additionally, in a cassette design with discrete sprockets, the complex recess and cutout features on the face of the sprockets, as well as the precise chamfered tooth features, may be more readily and economically produced by stamping these features onto individual sprockets before assembly into a cassette. The present invention achieves both a rigid and lightweight design that is contrary to the teachings of these prior devices. By using a single-piece truncated hollow cone design that ignores the art-perceived need for discrete sprockets, the present invention represents far more than a structural difference over these prior devices.